A major user group consisting of S NIH funded investigators with 9 projects, along with four NIH funded minor users, propose to purchase a Leica TCS SP Spectral Confocal Microscopy System. The work by these investigators requires state of art confocal capabilities that are not met by an out-dated 11 year old system currently available. These major projects require multiple excitation bands, tunable band-widths for emission, multiple channels for simultaneous imaging, improved sensitivity, real- time imaging capability and state of the art computer support for real time imaging and three-dimensional reconstruction. The confocal experiments proposed are expected to increase our understanding of clock regulated proteins and microtubule based motility in photoreceptors (Besharse, 2 projects), structural organization and signalling by integrins and PECAM-1 at the cell surface (Newman, 2 projects), structure and function of von Willebrand Antigen II (Montgomery, 3 projects), structural organization of and E-cadherin and polarity of retinal pigment epithelial cells (Burke) and three dimensional organization of viral factories during vaccinia virus assembly (Traktman). Each project addresses fundamental cell biological questions requiring a sophisticated confocal system in the context of a larger NIH funded project. The major user group is expected to use the new system for at least 80% of the available time during the three years of the proposed project; other NIH funded investigators including listed minor users will have access when the system is available. The new instrument will be set up within an existing imaging core facility at Medical College of Wisconsin. This imaging facility is supervised on a day to day basis by a full-time Biomedical Engineer who will assume responsibility for instrument maintenance and training of laboratory staff. During the project period, use of the new system will be controlled by an Advisory Committee consisting of the major users and chaired by the Principal Investigator. The institution will cover all renovation costs and service requirements for the instrument. After the project period, the long term care of the instrument for use of NIH funded investigators will be placed under the supervision of the existing imaging core facility.